1. Field of the Invention
The present invention relates to the field of integrated circuits. It more specifically relates to the detection of biological or chemical material.
2. Discussion of the Related Art
To detect the presence of biological or chemical material in an environment and quantify its concentration, the use of a detector formed of a semiconductor chip coated with a layer of a material capable of bonding to the biological or chemical material has been provided.
FIG. 1 shows such a detector 1 arranged in an aqueous environment 2. Aqueous environment 2 contains molecules 4 with a concentration in medium 2 which is desired to be quantified. Detector 1 is a MOS transistor comprising source and drain regions 6 and 8, as well as a gate layer 10 and a gate insulator 12. Insulated gate 10 is a detection layer comprising dangling bonds 14.
When a molecule 4 pairs with a dangling bond 14, an electric charge 15 appears in gate layer 10. The appearing of electric charge 15 generates an electrically opposite charge 17 in channel region 18 of transistor 1, gate 10 being further biased to a voltage Vp close to the transistor threshold voltage. The generation of charge 17 modifies the gate voltage of transistor 1, and thus its source-drain current. Quantifying this modification enables to deduce the concentration of molecules 4 in medium 2.
Such a detector 1 requires the presence of an external electrode enabling to bias gate 10 to voltage Vp. The reproducibility and the reliability of the concentration measurements are not guaranteed. Further, the sensitivity level of such a detector is not sufficient. When there is a small amount of material to be detected, the voltage difference generated by the appearing of charges 17 does not enable to sufficiently modify the gate voltage of the transistor.